Magnetic wave-amplifying repeater



Oct. 25, 1932. E. PETERSON MAGNETIC WAVE AMPLIFYING REPEATER Filed March30, 1929 5 6 0 Y 2 E )3 w/ L 5 F W F //v VE/V 70/? E. PETE/wow A TTUENE)Patented Oct. 25, 1932 UNITED STATES PATENT OFFICE EUGENE PETERSON, OFNEW YORK, N. Y., ASSIGNOR '10 BELL TELEPHONE LABORA- TORIES,INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK MAGNETICWAVE-AMPLIFYING REPEATER Application filed March 80,1929. Serial No.351,448.

The present invention relates to amplifying or reinforcing repeatersparticularly designed for use in a submarine cable although capable ofother uses as well.

An object of the invention is an amplifying repeater which, when onceinstalled, requires no attention, replacements or adjustments and which,therefore, is particularly suited to inaccessible situations, as in thecase of a submarine cable.

Among the requirements of such a repeater are: absence of moving partsand of parts which deteriorate appreciably with time, constancy ofoperating characteristics. rugged mechanical construction and ability towithstand excessively high compressional forces. Furthermore, the energyemployed in amplifying or reinforcing the signal must be suppliedindependent of local sources which would need replenishing from time totime.

The foregoing requirements are realized, according to the presentinvention, in a mag netic structure capable of being incorporated in orsuitably associated with the cable sheath and occupying smalldimensions. Assuming a submarine telephone cable which is to transmitfrequencies embracing the range 300 to 2000 cycles per second, a lowfrequency wave is supplied to the repeating point or points and is thereconverted into a wave of suitably high frequency to enablev the magneticstructure to introduce into the cable circuit a negative resistanceeffect in accordance with a magnetic modulator action which of itself iswell understood in the art. The negative resistance effect results inamplification of the speech wave traversing the cable. Since theattenuation of the cable is greatest for the upper frequencies of thetransmitted band, it may be necessary to reinforce only the upperportion of the frequency range, say the frequencies 1500 to 2000 cyclesper second. although it is within the invention to amplify some otherportion or the entire speech band that is being transmitted. The amountof amplification and the range over which it is effected is determinedby design and control of the system in a manner that will be clear fromthe description to follow.

The nature of the invention as a whole and its various aspects andobjects will appear more fully from the following detailed description,with reference to the accompanying drawing, in which Fig. 1 is a diagramillustrating certain frequency relations which may be utilized in asystem in accordance with the invention, Fig. 2 is a schematic diagramin simplified form of a complete system with a single repeaterillustrated and Fig. 3 is a detailed circuit diagram of a repeater suchas is indicated more generally in Fig. 2.

The invention is based on the known principle that if two fundamentalfrequencies are applied to a magnetic modulator a negative impedance tothe lower of the two fundamental frequencies is produced when theimpedance of the system is low to the lower side band and high to theupper side band frequencies. The magnitude of this negative resistancedepends upon the amplitude of the fundamental wave of the higherfrequency when the amplitude of this wave is large, and upon theimpedances offered to the side bands. The negative resistance to thelower fundamental frequency may be util zed to effect amplification ofthis component. The energy of the amplification is derived from thehigher frequency fundamental wave.

In Fig. 1 the horizontal axis represents frequencies for which the zeroof the scale is at the left. The range indicated as q is assumed to bethe range of essential speech frequencies to be transmitted. The range9' represents a portion of the higher frequencies of this range andcorresponds to the lower of the two fundamental frequencies mentioned inthe general example of the preceding paragraph. The upper fundamentalfrequency, which for convenience, will be referred to as the carrier, isindicated at p. The range 2p-q' represents the frequencies comprisingthe lower side band based upon double the carrier frequency, this sideband being produced by third order modulation. From the general examplegiven above it will be apparent that when the frequencies 9' and p areapplied to a magnetic modulator and when e system is made to present lowimpedance to the range 2pand high impedance to the upper side andfrequencies (219+ a negative resistance effect will be intr uced for therange 9.

If insteadof the range the entire range were applied to the modu ator toether with t 0 frequency and if low. impe ance were provided for t 9range 212-9 and high impedance for the range 2p+q then a negativeresistance would be produced for the entire range 9.

T e invention contemplates producing a negative resistance effect inseries in the signa 'ng circuit for the entire speech band, or for aportion of the band such as the range 1? comprising the uppermostfrequencies. T e effect of the negatlve resistance is, of course, toamplify the signal.

In the frequency diagram of Fig. 1 the carrier frequency p is observedto be above the upper limit of the speech range. In the case of asubmarine cable the attenuation would be quite high to a frequency ofthis order so that it is preferable to provide the frequency p at thevarious repeater points by transmitting over over the line a lowfrequency indicatedin Fig 1 as n lower than be as follows: .5 250 cyclesper second;

the range 9, from 300 cycles per second to 2000 cycles per second; therange 9, from 1500 to 2000 cycles per second; p, 2500 cycles per second.These values are to be taken as merely illustrative, of course, and notas limiting the invention.

Referring to Fig. 2 the line L extends between a west terminal WT and aneast terminal ET and may include a number of repeater points along theline, one only of these being designated at R. The line L may be anordinary telephone line, telephone cable, or a submarine telephone cablealthough the invention is not limited to the transmission of speech, butis suitable for other types of signals. The west terminal comprises aspeech transmitter 10 and a re ceiver 11 suitably coupled to the linethrough a conjugate connection for enabling transmission and receptionin anti-side tone relation, or with any desired degree of side tone. Thebalancing network 12 accurately or approximately balances the linedepending upon the degree of conjugacy desired between the circuits 10and 11. The filter 13 passes the frequency range to be transmitted overthe line L and preferably excludes frequencies outside of this range,which in the resent case is assumed to comprise the ban 300 to 2000cycles per second. This and the other wave filters shown throughout thesystem ma be designed in accordance with the princip es disclosed in U.S. patent to Campbell, No. 1,227,113, May 22, 1917.

There is also located at the west terminal a source of sustained waves14 of a fre quency of 250 cycles per second althou h it will beunderstood that this source may ave any convenient or suitablefrequency. The waves from source 14 are applied through thepotentiometer 15 and filter 16 to the line L, the filter 16 passingwaves of this freand excluding waves of higher and lower frequencies.

The speech waves traversing the line, upon arriving at a repeater pointB pass in part through the filter 17 and into the output of the magneticmodulator 18. It is assumed that the filter 17 passes the range 9' butexcludes the remaining portion of the speech range. Filter 19 allows thefrequency (i. e., 250 cycles per second), to pass into the harmonicgenerator 20 in which the carrier frequency p, (i. e., 2500 cycles persecond) is produced. This carrier frequency is applied to-the input ofthe modulator 18 and a number of new components are produced as a resultof the interaction in the magnetic modulator of the waves of frequency pand the range g. The impedance network 21 offers a low impedance to therange 2pg' and the circuit as a whole offers high impedance to the range2p+g'. As a result of this effect, as described more generally above,there is produced in series with the line L a negative resistance forthe frequency range 9' so that amplification of the range of thefrequency 9' is produced in the line L at the repeater point B. In asimilar manner this action may be produced at any desired number ofrepeater points along the line L.

In Figs. 2 and 3 the line is indicated as a two wire line. In the caseof a submarine cable it will be understood that a .single conductor witha ground return and with suitable terminal duplex or other connectionsfor enabling two-way conversation will be used. In this case the filter19, shown in shunt of the line, would be connected across from the cablecore to the cable sheath, the sheath forming the return for this wave.That is, in Fig. 3 the upper line conductor may be the cable sheath. Analternative manner of supplying this low frequency tions, although inpractice this low frequency wave may be sent out from both terminals.

Speech waves originating in the east terminal traverse the line L andwhen arriving at the repeater point B pass in partthrough the filter 17to the modulator 18 where they combine with the waves of the carrierfrequency produced in the harmonic generator 20 as a result of the wavesof frequency arriving from the west terminal. Amplification is producedat each repeater point for these westwardly transmitted speech waves inthe same manner as described above for the eastward transmission.

It will be clear from what was said above that the filter 17, ifdesired, may pass the entire speech frequency band and so produceamplification over the whole band. In a similar manner any portion otherthan g may be selectively amplified.

ircuits for carrying out the actions at the repeater point R as abovedescribed are shown in detail in Fig. 3. The filter 19 may comprisesimply a series tuned circuit comprising condenser 31 and inductance 32.The harmonic generator may comprise a single toroidal core with suitablewindings, but

has been shown as comprising a pair of toroidal cores 33 and 34 to forma balanced circuit. These cores have input windings 35 and 36 and outputwindings 37 and 38. Either the pair of windings 35 and 36, or the pairof windings 37 and 38 are wound in respectively opposite sense on thetwo cores 33 and 34. This produces a differential action and preventsthe frequencies from passing in either direction between the circuitcontaining the windings 35 and 36 and the circuit containing thewindings 37 and 38.

Due to the nonlinear BH characteristic of the cores 33 and 34, when thefrequency is applied to the windings 35 and 36, multiples of thesefrequencies appear in the circuits containing windings 37 and 38 one ofwhich is. of course the frequency 7. The balanced relationship of thecoils prevents to a large extent the harmonic frequencies in the.secondary circuit from passing back into the primary circuit and alsoprevents the input frequencies in the prima circuit from passing acrossto the secon ary circuit. This eases the requirements on the tunedcircuits. The circuit com rising the shunt arm 39 and the series arm 0aids in producing a large component of the 10th harmonic, i. e., thefrequency 7, assumed to be 2500 cycles per second, and in applying thisfrequency to the input windings of the magnetic modulator comprising thetoroidal cores 41 and 42. For this purpose the shunt 39 may be tuned tothe frequency and the series circuit to the frequency p.

The upper portion of the frequency band, i. e., g is selectivelytransmitted through the high pass filter 43 to the windings 45 and 46 ofthe magnetic modulator. Modulation takes place between waves of thefrequency 1) and the wave components of the signal contained in therange (1 both of which are applied to the magnetic modulator as has beendescribed. The impedance network 47 is designed to present across theouter terminals of'the magnetic windings 45 and 46 a low impedance tothe range 212-9 in this case extending from 3000 to 3500 cycles persecond and to present high impedance to frequencies both higher andlower than this range. The impedance network 47 may be designed inaccordance with well known filter theory to possess the proper impedancewithin the required frequency limits.

It is preferable to construct the cores of the harmonic generator andthe magnetic modulator of some magnetic alloy possessing highpermeability at low magnetizing forces such as is characteristic ofcertain of the nickel-iron alloys, examples of which are dis closed inU. S. patent to G. W. Elmen, No. 1,586,884, granted June 1, 1926. Oneadvantage of using such alloys is that the required magnetic effects maybe obtained by the use of cores and windings which occupy a relativelysmall space. This fact adapts the coils for mounting inside a submarinecable sheath. The various other inductances shown in Fig. 3 may likewisebe wound on nickel-iron alloy cores of suitable configuration to providethe requisite inductances in a small space. The condensers required areof relatively small capacity and may be designed to accommodate thespace within the sheath of a submarine cable such, for example, as bybeing made long relative to the width, or being curved around the cable.

It was stated above that the amount of amplification produced in thesignal waves is a function of the impedances afforded to the side bandsand to the amplitude of the carrier. The impedance characteristic of thenetwork 47 may be made to bear such a relation to frequency that thehigher frequencies in the range g are more strongly amplified than thelower. This is desirable because of the increasingly high attenuationafforded by the cable or transmission line at the higher frequencies.The invention therefore .contemplates designing the impedance of thenetwork 47 with reference to the attenuation characteristic of the lineL so that the band by either a constant factor or a variable factorrelated to the attenuation characteristic of the line. I

The dependence of the degree of amplification upon the amplitude of thecarrier frequency 7) offers a convenient method of controlling from aterminal station the amount of amplification to be produced at therepeater stations along the line or cable. For exam- .ple, in thecircuit diagram of Fig. 2 where the low frequency wave is shown as beingtransmitted from the west (or from each) terminal to all of the repeaterstations, provision is made in the potentiometer 15 for varying theamplitude of the wave of this frequency transmitted to all of therepeaters. The amplitude of this wave, of course, determines theamplitude of the wave of frequency 7; generated at each of the repeaterstations so that by controlling the potentiometer 15 the amplificationfactor may be controlled for each repeater. The preferred adjustment ofthe system is such an adjustment as will give a high degree of stabilityin each of the repeater circuits throughout a working range ofamplitudes determined by the controlling wave sent from the terminal,thus permitting stable operation of the repeaters at differentamplification factors within this range.

What is claimed is:

1. The combination with a submarine cable having a surrounding sheath,of a repeat er wholly included inside said sheath, said repeatercomprising magnetic modulator means for introducing a negativeresistance effect into the cable conductor within the frequency range ofthe signals transmitted over said conductor, and means to supply to saidmodulator means from a distance the energy of a sustained alternatingcurrent wave for enablin it to function.

2. submarine telephone repeater for a submarine cable comprisingwave-combining means whose action is wholly magnetic, and means tosupply to said wave-combining means a signal to be amplified and anotherwave derived from an alternating current wave sent over the cable, oflower frequency than the signal.

3. An amplifying repeater comprising means wholly magnetic in action forderiving from a low fre uency wave a wave of a high frequency suita 1efor combining with speech waves to reinforce them, and means whollymagnetic in action for causing interaction between the high frequencywaves and the speech waves to produce amplified speech waves.

4. In a submarine cable system means to send signal waves and a lowerfrequency sustained wave over the cable, means at a point in the cableto select the sustained wave and produce from it a wave of higherfrequency than the signal waves, a magnetic modulator, means to modulatetherein said high frequency wave by the signal waves, means presentingto the modulated components a low impedance to the lower side band ofthe modulated waves whereby said signal waves will be amplified, andmeans to apply the resultant amplified signal waves to the cable.

5. In a submarine cable system means to send signal waves over thecable, means also to transmit from a terminal station of the cable to anintermediate point thereof a sustained wave of alower frequency than thesignal, a magnetic modulator system at said intermediate point, andmeans including said modulator system thereat for utilizing the energyof said low frequency wave to reinforce said signal waves traversing thecable.

6. A system as defined in claim 5 including means for varying theamplitude of the low frequency wave sent from the terminal station tocontrol the degree to which the signal waves are reinforced at saidintermediate point.

7. In a submarine cable telephone system, means at a terminal station totransmit over the cable speech waves and a sustained low frequency wave,a magnetic modulator system at a point in the cable distant from theterminal. means at said point for applying at least a portion of thespeech waves to said magnetic modulator system, means for also selectingthe wave of low frequency and generating from it a wave of higherfrequency than the speech, a circuit for applying said higher frequencywave to said modulating system, the impedance and frequency relations ofthe modulator system being such as to produce amplification of theportion oi the speech waves applied to said modulating system, wherebythe speech waves traversing the cable are, in part at least, amplifiedat a point in the cable. 7

8. A system as defined in claim 7 in which means is provided for Varyingthe amplitude of the sustained low frequency wave. sent from theterminal station, whereby the degree of amplification at the said pointin the cable distant from the terminal is controlled.

9. In a signaling system, a line, means to send over said line a signaland a sustained wave of a different frequency from the signal, amagnetic modulator at a point in the line, means to apply to saidmodulator the signal and a sustained wave of higher frequency derivedfrom the sustained wave sent over the line, whereby modulation productsare generated in said modulator comprising upper and lower side bandsmeans presenting low impedance to currents of said lower sidebandfrequency range whereby said signals are amplified, and means to applythe resultant amplified signals to said line.

In witness whereof, I hereunto subscribe my name this 29th day of March,1929.

EUGENE PETERSON.

